Properties of r-modes in the Sun

Abstract

Global oscillations of the Sun (r-modes) with very long periods ∼ 1 month are reviewed and studied. Such modes would be trapped in an acoustic cavity formed either by most of the convective envelope or by most of the radiative interior. A turning point frequency giving cavity boundaries is defined and the run of eigenvalues for angular harmonics l ≤ 3 are plotted for a conventional solar convection zone. The r-modes show equipartition of oscillatory energy among shells which each contain one antinode in the radial dimension. Toroidal motion is dominant to at least the 14th radial harmonic mode. Viscosity from convective turbulence is strong and would damp any mode in just a few solar rotations if it were the only significant nonadiabatic effect. ‘Radial fine splitting’ which lifts the degeneracy in n is very small (20 nHz or less) for all n ≤ 14 trapped in the envelope. But, if splitting could be detected, we would have a valuable new constraint on solar convection theories.

Keywords

Viscosity Convection Convection Zone Solar Rotation Point Frequency

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